- Launch an Office app installed on your Mac, click on the application name (eg Word) menu and choose Sign Out.
- Close all Office applications.
- In the Finder, click on the Go menu and choose Go to Folder
- In the box, type: ~/Library
- Click on the Group Containers folder
- Locate the following three files/folders and drag them to the Trash
UBF8T346G9.ms
UBF8T346G9.Office
UBF8T346G9.OfficeOsfWebHost
- Empty the Trash and launch an Office application.
- Choose the activate option (NOT the sign-in option) and enter the correct MS Office credentials.
Update:
If this does not work (happens often with Big Sur) then you must take additional steps.
1. Log out of office applications
2. Remove the same three files as in step 6 above. Additionally, delete the other files next to it with Office in the name or microsoft in the name. may be up to 5 or 6 additional
3. Delete all office applications by moving them to the trash (not including OneDrive)
4. Launch keychain access and search for office. Delete all office keychain entries.
5. Reinstall office from portal.office.com
6. Launch word. It may still have an account preloaded. Sign out of this account.
7. Close word.
8. Open word and now try to activate office with their credentials.
9. If this works make sure they are still signed into OneDrive and Outlook.